Ytterbium (chemical symbol Yb, atomic number 70) is a soft silvery metallic rare earth element.[1] It is found in the minerals gadolinite, monazite, and xenotime. The element is sometimes associated with yttrium or other related elements and is used in certain steels. Natural ytterbium is a mix of seven stable isotopes.

Contents

Occurrence

Ytterbium is found with other rare earth elements in several rare minerals. It is most often recovered commercially from monazite sand (~0.03 percent ytterbium). The element is also found in euxenite and xenotime. Ytterbium is normally difficult to separate from other rare earths but ion-exchange and solvent extraction techniques developed in the late twentieth century have simplified separation. Known compounds of ytterbium are rare—they haven't been well characterized yet.

History

Ytterbium was discovered by the Swiss chemist Jean Charles Galissard de Marignac in 1878. Marignac found a new component in the earth then known as erbia and named it ytterbia (after Ytterby, the Swedish town where he found the new erbia component). He suspected that ytterbia was a compound of a new element he called ytterbium.

In 1907, the French chemist Georges Urbain separated Marignac's ytterbia into two components, neoytterbia and lutecia. Neoytterbia would later become known as the element ytterbium and lutecia would later be known as the element lutetium. Auer von Welsbach independently isolated these elements from ytterbia at about the same time but called them aldebaranium and cassiopeium.

The chemical and physical properties of ytterbium could not be determined until 1953 when the first nearly pure ytterbium was produced.

Ytterbium has three allotropes, called alpha, beta, and gamma. Their transformation points are at −13 °C and 795 °C. The beta form exists at room temperature and has a face-centered crystal structure while the high-temperature gamma form has a body-centered crystal structure.

Normally, the beta form has a metallic-like electrical conductivity, but becomes a semiconductor when exposed to around 16,000 atm (1.6 GPa). Its electrical resistance is tenfold larger at about 39,000 atm (3.9 GPa) but then dramatically drops to around ten percent of its room temperature resistivity value at 40,000 atm (four GPa).

Isotopes

Naturally occurring ytterbium is composed of seven stable isotopes—Yb-168, Yb-170, Yb-171, Yb-172, Yb-173, Yb-174, and Yb-176—with Yb-174 being the most abundant (31.8 percent natural abundance). 22 radioisotopes have been characterized, with the most stable being Yb-169 with a half-life of 32.026 days, Yb-175 with a half-life of 4.185 days, and Yb-166 with a half life of 56.7 hours. All of the remaining radioactive isotopes have half-lifes that are less than two hours, and the majority of these have half lifes that are less than 20 minutes. This element also has six meta states, with the most stable being Yb-169m (t½ 46 seconds).

The isotopes of ytterbium range in atomic weight from 150.955 u (Yb-151) to 179.952 u (Yb-180). The primary decay mode before the most abundant stable isotope, Yb-174 is electron capture, and the primary mode after is beta emission. The primary decay products before Yb-174 are element 69 (thulium) isotopes, and the primary products after are element 71 (lutetium) isotopes. Of interest to modern quantum optics, the different ytterbium isotopes follow either Bose-Einstein statistics or Fermi-Dirac statistics, leading to interesting behavior in optical lattices.

Applications

One ytterbium isotope has been used as a radiation source substitute for a portable X-ray machine when electricity was not available.

This metal could also be used to help improve the grain refinement, strength, and other mechanical properties of stainless steel.

There are few other uses of this element, such as in the form of ions in active laser media.

Precautions

Although ytterbium is fairly stable, it nevertheless should be stored in closed containers to protect it from air and moisture. All compounds of ytterbium should be treated as highly toxic although initial studies appear to indicate that the danger is limited. Ytterbium compounds are, however, known to cause skin and eye irritation and may be teratogenic. Metallic ytterbium dust poses a fire and explosion hazard.

See also

Notes

↑ The term "rare earth metals" (or "rare earth elements") is a trivial name applied to 16 chemical elements: scandium, yttrium, and 14 of the 15 lanthanides (excluding promethium), which occur naturally on Earth. Some definitions also include the actinides. The word "earth" is an obsolete term for oxide. The term "rare earth" is discouraged by the International Union of Pure and Applied Chemistry (IUPAC), as these elements are relatively abundant in the Earth's crust.

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